In the previous DIY Science project, DIY Vortex Stabilized Gliding Arc Discharge, I demonstrated a very simple build for a nonthermal atmospheric forward vortex stabilized gliding arc discharge plasma system, made from scrap parts. In this project, we will take this previous build to the next level, and use it to explore a practical and very exciting application of this technology for advanced combustion systems. I will demonstrate the principles of plasma assisted combustion using nonthermal atmospheric gliding arc discharges, and explore some very simple experiments that exemplify some of the unique features and advantages of using this technology for plasma assisted combustion.
PLASMA ASSISTED COMBUSTION OVERVIEW
Before we get into some of the example tests and demonstrations, what exactly is plasma assisted combustion? In simple terms, plasma assisted combustion (PAC) is the process of using a plasma (often in the form of nonthermal/nonequilibrium plasmas) to enhance or assist combustion processes. PAC is a complex and intensively multidisciplinary study that covers a wide range of engineering and sciences, from combustion, to chemistry, plasma engineering, thermals/fluids, and has a wide range of applications in industries such as aeronautical, aerospace, power generation, propulsion, and many others.
PAC is a very complex and involved multidisciplinary field. While I could go into the extensive details about this field here, there are much better resources already available on the field of PAC that are far better explained by the leading researchers in the field themselves. If you are interested in learning more about PAC, there is a fantastic lecture series freely available from the Princeton CEFRC Combustion Summer School. This multi-day, multi-lecture series is led by Dr. Ju, a leading researcher and expert in PAC. The full lecture series is posted on Youtube and can be found here: Plasma Assisted Combustion – Ju. I highly recommend watching the lecture series, which covers a tremendous amount of in-depth principles, physics, and applications of PAC.
Another great resource on PAC and related technologies can be found at the International Plasma Technology Center, which has a significant amount of resources on plasma assisted combustion technologies. This effort is led by Dr. Igor Matveev, another leader and pioneer in the field of PAC, which aims to promote resources, expertise, research, and collaboration in the field of PAC.
What are some practical applications of PAC? PAC can be used for a wide and diverse range of applications, ranging from fuel reforming, hydrocarbon cracking, cleaner-burning combustion cycles, combustion efficiency improvement, cool flames, and enhanced ignition and flame stability in extreme environments, such as igniters for scramjet engines, or inside gas turbines.
As mentioned before, often times PAC relies on the use of nonthermal/nonequilibrium plasmas. The most common types of nonthermal plasma used in PAC include dielectric barrier discharge (DBD), gliding arc discharge (GAD), and nanosecond pulse discharges. Depending on the goal and system involved, there are countless ways to implement nonthermal plasmas for PAC. For this simple DIY Science demonstration, we will look at one of the simplest nonthermal plasmas to form – the gliding arc discharge. In fact, I have provided several gliding arc discharge builds in prior DIY Science pages, thoroughly exploring the concepts and principles behind GAD technology. For the following demonstrations, I will be showing the use of a forward-vortex stabilized gliding arc discharge as a plasma fuel nozzle to explore PAC and the effects of the plasma on flame dynamics, burn stability, and throttle control. For reference, you can actually see a video of a commercially produced plasma fuel nozzle here, from Applied Plasma Technologies.
Despite the fact that PAC is a very complex and involved field, combining combustion, chemistry, and plasma engineering, we will see that a very simple tabletop setup can be built for almost no cost to explore this unique and exciting field. The demo unit shown below can be further improved and enhanced to make a fully instrumented tabletop combustion testing platform for more advanced DIY combustion studies.
DEMONSTRATION 1 – BURN COMPARISON
In the first two demo videos, we explore the difference in burn dynamics between a standard flame and a flame using plasma assisted combustion. The fuel used is propane, with a small blower to provide air. The plasmatron is the DIY Vortex Stabilized Gliding Arc Discharge system. In both tests, constant fuel and air flow is supplied. The fuel is ignited, and the plasma power is cycled on and off to compare the difference between the normal flame and the plasma assisted flame. Immediately, you can observe a radical difference in flame characteristics between the two modes of operation. While the regular burning flame is a more spread, billowing flame, when the plasma is turned on, the flame rapidly constricts itself, forming a tighter and radically different burn. The first video shows a test using moderate fuel flow. The second video is a shorter test that shows the use of much more fuel, resulting in a larger flame plume.
DEMONSTRATION 2 – THROTTLE CONTROL
In the next two videos, we explore how plasma assisted combustion can affect throttle control of the burn. In the first video, fuel is cycled from low to high several times for both a normal burning flame and a plasma assisted flame. During the normal flame burn, at the lowest end of fuel input, we see some instabilities arise in the flame. However, with the plasma assist on, these instabilities disappear, and the flame throttles very consistently and smoothly from an extremely low fuel condition to full fuel input. In the second video, the plasmatron is first started, and fuel is slowly introduced until max burn is established, then throttled back down to a no fuel condition. In this case, we see a very smooth transition into ignition to max burn.
Now that we have established a very simple way of experimenting with a rather advanced technology of plasma assisted combustion for a very low cost looking at a simple plasma fuel nozzle, what can be done to further explore this exciting application of nonthermal plasma technology? The system can first be further refined with a better designed injector and nozzle. Additional tangential ports can be added to mix air, fuel, and other process gases separately. The plasma fuel nozzle can be mounted inside of an instrumented flame tube, with thermocouples and gas sensors such as CO to look at the characteristics of the combustion process and collect data between a normal burning flame and a plasma assisted flame. The system can also be scaled to a smaller, more compact unit, or expanded to a much larger burner. Different output nozzles, swirl configurations, and electrode materials can be explored. The system can also be converted to a reverse-vortex stabilized gliding arc discharge to see how reverse vortex stabilization differs from forward vortex stabilization. By using high air-speed sources, such as a leaf blower, areas such as subsonic ram air ignition and flame stabilization can also be experimented with. In this case, other methods of ignition such as planar electrode igniters for high airspeed ignition can be explored. For the ultimate test, plasma assisted combustion can be integrated into actual turbines or jet engines, either small model jets or turbocharger-based turbines, to explore the effects of the technology on high pressure combustion in turbomachinery. In future plasma assisted combustion project examples at Applied Ion Systems, I will be exploring more engineered nozzles, as well as system instrumentation for data collection on burn characteristics, and high speed airflow burn stabilization under very lean conditions.